Group decisions: From compromise to leadership in pigeon homing

Social animals have to make decisions that affect not just themselves, but everyone in the group. For example, when embarking on a journey together, individuals must agree on the route–a difficult task if group members cannot assess who are the best navigators or who is best informed about possible routes. Is a “democratic” average of everyone's opinion best? Or is it better to trust a leader? And what circumstances influence how animals decide which of these strategies to follow?

In the new study, the researchers used miniature GPS tracking devices to follow the homing flights of pairs of pigeons, where both individuals had their own, previously established preferred routes leading back to the loft. When the birds were released as a pair, and when the two preferred routes were not very different, the conflict between birds' preferences was resolved by a mutual compromise in which both birds flew by an intermediate route. When preferred routes of the two birds differed greatly, however, the compromise position was replaced by a scenario in which the preferred route of one bird–who would emerge as the “leader”–was followed by both birds for the rest of the journey.

Using a mathematical model to better understand the basis of the paired birds' navigation choices, the researchers found that both forms of decision-making could emerge from just two simple forces acting simultaneously on the pigeons' behavior: “move toward your familiar route” and “move toward your partner.” In cases of small disagreements about the route, these two forces, or rules, lead to mutual compromise. However, when preferred routes are sufficiently different, behavior resembling compromise turns to behavior characterized by leadership as one bird abandons its own route to instead follow that of its partner. The outcome of the mathematical modeling therefore indicated that compromise and leadership are two outcomes of the same decision-making process.

In another aspect of the study, the analysis of pigeon behavior showed that birds flying in pairs seem to take more efficient routes home than those flying alone, suggesting that in addition to safety in numbers, traveling in the company of others brings navigational benefits to individual group members.